Iron oxide reduction



May 14, 1957 H. FREEMAN IRON oxIDE REDUCTION 2 Sheets-Sheet 2 R. m N...m m A N V M M N s r out Our HM l. E M

, e nm :lv Our 30D HO May 14, 1957 H. FREEMAN IRON oxIDE REDUCTION FiledApril 9, 1954 Y Y @at BJQU w ..2 v ...vn

.IRON OXIDE REDUCTION vHorace Freeman, Cap-de-la-Madeleine, Quebec,Canada Application April 9, 1954, Serial No.4 422,187

13 Claims. (Cl. 75-3) This invention relates toprocesses for directlyvreducing ironcres vand other Viron oxides by means of carbon orcarbonaceous material to form iron, and'more particularly pellets ofsponge iron which may be ground' to form iron powder or used as meltingstock.

Heretofore eiforts to continuously and directly reduce iron oxide toform sponge iron or the like in rotarykilns or other furnaces, haveinvolved excessive expensesfor fuel and the serious difficulties thatthe furnace-charge would sinter andv stick in lumps and to thefurnacewalls, forming agglomerates ora product still embodying 'considerableamounts of oxide, ash and of the carbon used as reducing agent and asfuel.

The present invention, however, provides an economical method ofovercoming these difficulties and making possible the direct .andsubstantially complete reduction of iron oxide to sponge iron containingforexample from 0.01 to 0.2% of carbon and free of any particles ormasses of the carbon used as fuel, orthe ash thereof.

Briey the present invention involves rst grinding the iron oxide or oreto a powder and then formingsame into pellets. Such pellets are fed into-a rotary kiln or other suitable furnace along-with fine carbon materialof a nature suchthat its ash does not fuse or sinter at the reactiontemperature in the furnacey (190D-2100" F.) Airis admitted to thefurnace at a ratev limitedso as to provide only enough to reactwith theamount of carbon necessary to produce the heat requiredforreducing allof the iron oxide to iron. Some excess carbon is introduced anddischarged vfrom the'fuinacewith" the reduced sponge iron pellets, butsuch excessds readily separated Vfrom the vpellets by screening. or'bymagnetic separation. The excess carbon lin the `furnace acts promptly toreducefth'e carbon dioxi'de'formedlby the reaction, to carbon monoxide,`so that thepelletsremain in an atmosphere in 'thefurnacelargelyfconstituting nitrogen and carbon monoxide, untilthey'a're'reduced to sponge iron. Then the pellets, togetherwith theexcess carbon, are advanced throughr a cooling'zone while'stillremaining in an"atmospherelargely'comprising nitrogen and carbonmonoxide untilthe mixtureis cooled sufficiently so that it maybedischarged` without danger of re-oxidationof the iron.

In order to absorb any volatilesulphur compounds which may be evolvedupon the heating ofthe carbon fuel used, and sothat the sulphur may notenter the reduced iron, an amountv of lime," lime hydrate, limestoneVor'dolornite, for example, amounting 'to about-2v to 20% by weight ofthe carbon, is preferablyadde'd tothe furnace charge;

In order to cause the carbon more readily-to react withthe oxygen ofthe-.air in the furnace, wherebyhigher concentrations of carbon monoxidemay be maintained at lower temperatures, a small amount of a .catalystsuch as sodium carbonate orsodiumaluminate is also ,Preferably added tothe charge. 'Ihis enabIeshighercOnCen- 'trations of the vmonoxide to'beobtained'thanwold be United States Patent O 2,792,298 Patented May 14,1957 ice .pssible-without the use of such a catalyst, thereby making itpossible to obtain complete reduction of the iron oxidefat temperatureswell below the fusion point of the'ash'of the carbon used. The amount ofsodium `carbonate may vary from about 0.5 to 1% by weight of the carbonused. The carbon, preferably in the form of anthracite coal fines,together with the lime or lime- `stone ordolomite and sodium carbonate,are mixed and ground together preferably to a neness 'to pass a 20 meshscreen, .for example.

Other and more specific objects, features and advantages of theinvention will appear from the detailed description given below taken inconnection with the accompanying drawings which form apart of this'specifi- `ferred arrangement of apparatus forcarrying'out theinvention,v the reducing zone with this apparatus constitut- Fig. 2illustrates somewhat schematically, an alterna- `tive form`oftu'nne'l-like furnace with aconveyortherethroughwhich may besubstituted for' the rotary arrangement of Fig. 1; and

Fig. 3:-shows somewhat schematicallyin vertical section a Herresholftype of rotary rabble furnace which may .in .some' cases'be used in lieuof the rotary kiln arrangement.

The iron ore or oxide to be reduced may be in any well known form, suchas magnetite, its industrial counterpart rolling mill scale, or itmaycomprise the iron oxide cinder resulting from the combustion of ironsulphide ores, for example by flash roasting in the recovery of sulphurdioxide from such sulphide ores. Such cinder is presently available atlow cost in large quantities for which there is little or no market, yetdespite its sulphur content, it may be economicallyn'sed in carrying outthe present invention, since the sulphur will be roasted off in theprocess. The invention has been carkiln ried out in one of itsembodiments `by theY use of ordinary commercially available rolling millscale, and in another embodiment by vusing a high grade Brazilianhematite ore. The oxide used may or may not contain appreciablylquantities of non-ferrous material such -as silica gangue withoutunduly interfering with the process, except that it is understood thatif highly pure iron 'is required, a highly pure oxide or orevshouldbeused `mesh screen or finer, so that the later pelleting or briquettingoperation will proceed efficiently, a proportionvof finematerialaidingsuch formation. Pelleting is accomplished (and is preferred tobriquetting) by adding10% of water to the dry material, or bydewateringto 10% moisture if it is already wet. The binding materialused may comprise ordinary wheat flour, molasses, silicate of soda,sultite liquor, lime, caustic soda or magnesia, any of which, used inthe order of .5% to 2% of the ore weight, will give a sufficiently hardpellet without adding unduly to .theirnpurity of the product. But wherehigh purity of the iron product is required, obviously a binder shouldbe used which will yield as little as possible by way of impurities uponheating of the pellets.

The damp sticky mixture is then fed to a rotating drum as at 11 (whichmay be similar in construction to that of an ordinary rotary roastingkiln) by a suitable conveyor as at 12 having a jagged feed screw 13shaped to break or chop the mixture into small pieces which becomerounded approximately into spheres by the rolling action as they passthrough the drum 11. The size of these spheres or pellets may becontrolled by regulating the moisture content of the mixture or byaltering the feed screw configuration to change the cutting laction andthey may be varied from as small as M6" in diameter to as large as l to2 inches or more. But the best results,

lfor rapid reduction later in the process, are obtained with smallerpellets of a size in the neighborhood of about 1A" in diameter orsometimes less. In 'any case, they should be suciently larger than thecarbon particles which are to be later mixed therewith, so that they maybe cleanly separated from the excess carbon as by screening orotherwise.

Such pellets are damp and soft 'as iirst formed, and

although they may be dried in the same rotarydrum 11 in which they areformed, preferably the drying is completed later with as littleagitation as possible to`prevent breaking and dust formation. Suchdrying may be accomplished on a belt conveyor or tunnel dryer 'at 12.

The dry pellets may be used directly, but I have found it advantageousin some cases to give them a further treatment by roasting them at hightemperature. This roasting may be effected without the adition of fuel,if the oxide used is of the magnetic ore type, that is, ferrous oxide.The conversion of ferrous oxide to ferrie oxide is accompanied by thegeneration of heat, under the proper conditions, sucient to bring thepellets to incipient fusion, the reaction being as follows:

column or bed of the pellets is kept in motion as by continuous feed anddischarge, there will be no sticking of same together and in coolingthey will be extremely hard, porous, somewhat vitreous with some hollowcores. It has been found that pellets so prepared completely resistabrasion in the presence of the coal fines during the reducing processhereinafter described and the pellets now being fully oxidized to theferrie oxide state, it has been found that they are more rapidly reducedthat the magnetic forms of oxide.

Either the dried pellets or dried and roasted pellets, if they have beenprepared with a binder such as flour or molasses, free from suchmetallic bases as soda, lime or magnesia, will upon reduction to iron,swell considerably, giving pellets of sponge iron twice as large orlarger than the original oxide pellet and though this is advantageousfor some uses, as when a very tine, light, porous iron powder isrequired, it is undesirable for other uses where larger particle sizeand higher density is required. This swelling may be entirely preventedby using one half of one percent by weight of the ore, either of soda,

lime or magnesia as a binding agent in the pelleting operation, with orwithout the use of organic binders. These bases are found to combinewith the iron oxide in the high temperature self-roasting operation withthe result, that, in later reduction the pellets do not swell and may becomminuted to give a dense metallic powder of large particle size, dueno doubt to the bonds effected by the fused base addition.

It will be obvious that if hematite or ferrie oxide be the ore used itis not capable of further oxidation and the pellets thereof will not beself-roasting, but it has been found that if approximately 7% of itsweight of the reduced metallic iron powder be added to this type of orein the grinding operation, it will yield a mixture behaving for theprocess of this invention as if it were the ferrous or magnetic oxideand is then self-roasting.

A further and important feature of the use of finely divided ore formedinto pellets and roasted as above described is that they are freed ofany sulphur content in the roasting operation and the finished balls orpellets are substantially round, hard, vitreous but neverthelessextremely permeable to the reducing gases.

Having now formed the pellets as above described, same are then mixed asin a hopper 13 with approximately 40% of their weight of carbon in theform of substantially dry anthracite coal fines of a particle sizeconsiderably smaller than the pellets so that the excess may later bereadily separated from the reduced pellets by using a screen of a sizeto retain the pellets and to pass the carbon particles. Anthracite coalnes or any suitable carbon having refractory ash may be used, that is tosay ash which, in the presence of additives as described, is infusibleat the temperature of reduction.

Preferably anthracite is used since its ash has a high melting point, itis inexpensive, abundant and usually so low in sulphur that only a smalladdition of lime is required to retain this sulphur from entering theiron. Welsh anthracite as well as Pennsylvania anthracite has beensuccessfully used. It is usually advantageous to add up to one percentof sodium carbonate to the coal since its use greatly increases theconcentration of monoxide at temperatures around 1900-2100 F. which areused for reduction. It has further been found that a substantially dryreducing agent, low in volatile hydrocarbons, gives best result sincethere is not sucient formation of water vapor in the combustion toeffect condensation in the operation of cooling the reduced iron.

The mixture of pellets and substantially dry coal fines s now fed as bya conveyor 14 to the charging end of the reduction furnace. A rotatingkiln as at 1S is preferred, which may be of alloy steel externally heatinsulated and used without a refractory lining or it may be a suitablyinsulated steel kiln with a brick lining as at 16. Such a rotary kilnhas an extension 17 which is suitably water cooled as by sprays 26 andin which extension the reduced pellets, excess carbon and the protectinggas resulting from the reaction, travel together ,to the discharge end18.

v A stationary tunnel type furnace as at 20 (Fig. 2) has been used witha continuous moving stainless steel conveyor belt or belt 21 forming ahearth, or having a hearth rof vibratory type, and in either case thefurnace is pro- Avided with a water cooled prolongation as at 22.Alternatively the well known Herreshol type of multiple hearth furnacemay be used as shown in Fig. 3 having hearths superimposed one aboveanother and with rotatable rabvbles tokcause the charge to move from thetop down and across successively lower hearths, the lowest of which asat 23 may be water cooled by cooling coils 25.

Whichever type of furnace be used it is essential that its coolingprolongation or section be connected directly with a gas tightconnection to the heating section of the furnace so that as the reduced(iron) pellets and excess coal pass from the heat reducing zone theytravel preferably cocurrently with the exit gases into and through thiscooling section and are therefore cooled 4nearly to atmospherictemperature in the same gas composition (as to CO:CO2 ratio) as wasdeveloped at thc end of the reduction zone. Testing of the gases for theratio of CO toCOz content will indicate if a sufficiently high carbonmonoxide content is being maintained during the cooling so that thesurfaces of the pellets are Inot reoxidized in the cooling process. Ifthe ratio of ,carbon monoxide to carbon dioxide be as 2:1 at the end `of`the reducing'zone and no air oroxygen bel admitted 'tothe cooling zone,then this gas compositionfwill continue tobe reducing towards thepellets as they cool and they will discharge to' the atmosphereV withoutoxidation. They may be carried by conveyor 26 to suitable screening ormagnetic separating apparatus 27 to be therein separated from the excesscoal and become substantially free from carbon. The pellets may `.thenbe ground to form iron powder, in a grinder 28. It has been found thatlarge quantities of pellets so prepared Iwill contain not more than 0.2%carbon and may have as low as 0.01% carbon.

The heated reducing section maybe of any desirable length ordiameter,according to capacity required, but its speed of rotation (forexample 1 R. P. M.) and rate of feed requires a time of travel in thereducing zone of not less than about 80 minutes if the pellets are assmall as V16" in diameter, while pellets as large as 2" in diameterrequire somewhat in excess of Z-hours for complete reduction.

Carbon dioxide which is formed in diminishing quantity as the chargeproceeds toward the discharge end is reduced to monoxide by the excessof hot carbon particles.

It is found that by charging in this manner the ternperature may bemaintained without difficulty at the desired reducing level (11900-2100F.) :throughout the length of the furnace by means of a singlecontrolled supply of air at the inlet end, since the heat rapidlygenerated at the charging end is rapidly absorbed by the cold charge andby the heat absorbing reaction at that end, while the monoxide formedacting upon the hot, nearly reduced pellets toward the discharge' endevolves heat, which is however counteracted by the heat absorbingreduction of the carbon dioxide'by still hot carbon at that end.

The gases leaving the cooling zone at outlet 18 are received in ahousing 30 and are drawn through a duct 31 by a blower 32 from whichthey pass through an air preheater 33 to a flue connection 34. Since thegases from the process have a substantial carbon monoxide content,combustion air is preferably introduced as through a connection 35 topermit burning of such monoxide before the gases are discharged fromtheflue.

" The air which is introduced into the reducing zone A is suppliedthrough any suitable metering means, through a'duct 36, and is preheatedin the preheater 33 lbefore being carried into duct 37 from which theair may be discharged into the furnace through an intakepipe 3Ssurrounding and concentric with the conveyor 14.

VAs indicated at 40, the intake end of the furnace may be `equipped witha suitable oil or gas burner'. for use in bringing the interior of thefurnace up to the required vtemperature, for example 1900-2100 F., forstarting operations. But after the reducing reaction Iis properlystarted, the operation of the burner is discontinued.: Al-

'though the` gases in `the furnace' travel "preferably cocurrent withthematerial of the charge, it will bev found thatthe intake region withinthe furnace will bemaintained at the required ignition temperature duetoreverberatoryaction from the wall or roof of the furnace "atthe chargingend and the fact that hot portions of the `charge,v asagitated in thefurnace, will'partially fall back toward the intake region.

Itwill be`understood'that the conveyortunnel type `of furnace of Fig. 2maybe' fed if desired .inthe same `manner as the rotary kilnof Fig. l'and that the gases at the exit end may hev received in a housing as`at30 and then conducted to afpreheater before going to the And the.product from the furnace of'Fig. 2 maybe carried by aconveyor 26', toscreening 'and grinding means as per.Fig. l.

"In the furnace of Fig. 2` electrical heaters, for example,

as ati'; may beinstalledfor bringing thefurnace vup IV`totherequiredH-startingz VtemperatureV an'dZin-the furnace" lfof/Fig. 3 avburner 1asfat'40" may *be-provided forthe .1same purpose. .'In the`latter furnace the upper hearth 441,1.if desired, mayxbeused forpreheating Ethe charge .asfreceived'from ahopper 42 and a'conveyor 43.The exit gases and the mixture coming out of the outlet `conduit '44 ofythefurnace of Fig. 3. may be treated the same :as withvthe furnacesof'Figs. 1 and 2.v `If desired, in-

stead .ofrmeteringthe air supply tor each of thefurnaces :beforertheairenters, the-rate of` air `supply may be regulated merely.v ybyvarying Ithe speed or capacity `of `the blower which `supplies/.the air.

vAn important aspectof the present invention involves .'the relativerates` at which the pellets, carbon, and more particularlyfthe air; areintroduced into the furnace. It

iconversionwofthe'carbon `to gaseous carbon monoxide.

The actual reduction of the iron oxide is effected by the action-of'this gas 1upon the ore lparticles, vlresulting `in metallic iron andcarbon dioxide as the direct products.

Forthe reactionto proceed to completionv enough heat.must.be:suppliedvto reduce such'carbon dioxide tomonu --oxide by meansof ffree carbon.

The .'reactionfof carbon monoxideupon iron oxides is itknown .-to be`exothermic` provided the gas'used and the iron ore be preheated to thetemperature -ofwreaction ,(1900-2,100 F.) and `the temperature of. theproduct (i1-on)fwil1 rise. Y It is known that a considerable excessofcarbonemo'noxide. must be utilized to complete the reduction', lin theabsenceV ofhot solid carbon, andthe excess required is an obstacle tothe economic use'of `separately prepared monoxide" (such as monoxidefrom agas producer) upon iron ores in the absence offree carbon.

With the present invention the carbonin the mixture is kignited and theair `supply is so controlled thatthe carbon is burned -to carbonmonoxide while developing enough heat in the process to supply thatwhich is re- .fquired to bring the coal, the air and the pellets to thereacting temperature and also that which is required to complete thereduction reaction, according to the heat requirements of the reactionof carbon upon iron oxide.

- When solid `carbon is used to reduce iron oxidethe total heat requiredwhen commencing vwith cold raw materials is 1800 B. t. u.s per pound ofiron produced. If the heat be generated Within the charge by'causingcombustion to yproceed-in such manner that only carbon'monoxide begenerated as follows:

ZC-i-Oz: 2CO

there will be generated -approximately4400 B. t. u.s per .pound-ofcarbon oxidized. Thus for each 100 pounds -of ore pellets inthe chargethere will be required, if the ore But an excess of carbon amountingpreferably to about 12 Aadditional pounds of coal is used for reasonsfurther explained below.) The combustion of this 28.6 lbs. of carbonrequires the use of approximately cubicfeet of .air for each pound ofcarbon and therefore air is blown in thecharging end or drawnthrough byinduced draft at the discharge end and controlled by an analysis of thedischarge gases, so that it may be proportioned to the amount of coaland pellets being charged. The exact amount of air may be regulated byobserving the nature -of the pellets discharging from the cooler as wellast by gas analysis.

If the pellets show incipient fusion of the metalthe :28.6 lbs. ofcarbon reduction temperature wllbetoo high and itY may be lowered byrestricting the air, or the temperature thereof,

, and conversely if the pellets are not sufficiently Well reduced, thetemperature is too low and may be corrected accordingly.

By generating the required heat in thismanner, the charge will be heatedto reacting temperature and it is important to note that thereducti-onwill commence at the charging end Where the greatest amount ofheat is required and where it can rapidly be absorbed. Such reduction iseffected by the gaseous diffusion of monoxide into the porous pelletswith simultaneous Igeneration of heat within the pellets and theevolution of carbon dioxide. In order that the reduction may continue tocompletion, however, it is necessary to maintain a high concentration ofmonoxide in the gases surrounding the pellets. This may be done byrenewing or changing the vsupply of monoxide but, in this process, iseffected by having present with the partially and completely reducedpellets an excess of hot carbon particles which serve to reduce thecarbon dioxide as fast as it is ditfused from the pellets.

A further function of the coal particles and of Ithe refractory ashparticles is that they serve as `an unfused interfering phase betweenpellets of reduced iron and prevent them from sintering together, orfrom adhering to the walls of the furnace, or to the furnace conveyor,if such be used.

It has been found in practice that the use of 40 lbs. (or in some casesfrom 35-50 lbs.) of carbon if in the form of the finely groundedanthracite, is 'ample to provide the required excess when used forexample with 100 lbs. of pure hematite. Anthracite nes or coke which maybe sutiiciently reactive without the addition of a catalytic agent andalso be sufficiently low in sulphur content that same also may not needthe addition of lime as a sulphur retainer. However, it is noted that ifthe carbon iines are not suiciently reactive to form monoxide theladdition of a catalytic agent such as sodium carbonate, with or withoutlime, does not materially lower the fusion point of the ash of saidmixture and is most effective in maintaining high monoxideconcentration.

The well known experience of sintering or sticking of the charge in theoperation of furnaces, particularly rotary furnaces, for sponge ironproduction is due to a variety of causes as follows:

(l) The. presence, or production of, oxide fines Within the chargeresulting in the reduced metal fines becoming reoxidized and fusingtogether as a partially oxidized mass.

(2) The fusion of the ash -of the reducing agent.

(3) The coking of the fuel when such material as raw bituminous coal beused.

With the present invention,- however, these effects are avoided (a) bythe use of the ore in pellet form, so hard that it is not abraded by themotion of the charge in such furnaces as rotary kilns or multiple hearthfurnaces; (b) by the use of non-coking reducing carbon (coal) in suchsmaller state of division than the pellets of ore, or of reduced iron,that same acts as -an interfering phase between the pellets, suchreducing agent being selected so that even with the addition ofcatalytic agent or limestone its ash residue is non-sticky and notfused.

The process of this invention may be distinguished from prior knownprocesses essentially by the following combination of features:

(l) The preventing of sticking or sintering of the charge by preforrningthe iron oxide into hard' pellets which do not disintegrate during thereduction or form fine iron particles, and by using a form `of carbonsuch for example as anthractie, from which the ash has a melting pointwell above the temperature employed for reduction and which does notadhere to the reduced iron pellets.

,'(2) Utilizing the carbon reducing agent in such manner that all of theheat required for the reduction of the iron oxide starting with a coldcharge, may be provided by burning enough of the carbon in the chargewith a limited amount of air to form carbon monoxide and maintaining thepreponderance of carbon monoxide in the gases by means of the presenceof excess hot free carbon in a finely divided and sutciently reactivestate.

(3) Rapid heating of the pellets and carbon at the charging end of thereduction furnace where most heat is required and advancing the chargepreferably although not yalways necessarily co-current with evolvedgases which are maintained with enough `carbon monoxide so that a highlyeffective reducing action on the iron oxide persists, and then coolingthe resulting mixture in an atmosphere constituting the gaseous productsof the reaction which prevent oxidation of the iron during its cooling.

(4) Separation of the reduced oxide pellets from the excess carbon byinsuring that the pellets are so substantially larger than the carbonparticles, a complete separation may be accomplished by screening ormagnetic means.

The following is an analysis of typical iron products made in accordancewith the invention from mill scale:

Carbon 0.01 to 20% maximum. Iron oxide (unreduced) as 0.5 to 1.5%maximum.

FeaOi.

Sulphur 0.02 to 0.04%. Phosphorus 0.03 to 0.06%. Metallic iron 98.4 to97.50.

The mill scale was ground with the addition of one-half of 1% by weightof lime and then made into selfroasted pellests as above described.yThese pellets were reduced by the process of the invention by adding35% by weight of anthractite coal thereto which would pass a meshscreen, said coal having been intimately mixed with 0.5% sodiumcarbonate and 5% of lime hydrate. The resulting pellets of the abovestated compositions may be disintegrated to yield iron powder suitablefor the purposes of powder metallurgy.

Upon using an exceptionally pure ferrie oxide ore, for example onecontaining lcss than 0.4% of silica, pellets have been produced andreduced with 35% prepared anthracite, to have the following analysis:

From the above examples it will be seen that the separation of thepellets from the excess coal is complete and that the reduction issubstantially complete.

Similar results are obtained if lower grade oxide such as pyrites cinderbe used except that although an iron with quite low carbon content isobtained it is less pure due to the gangue, amounting to 5% which ispresent in the cinder. Such a product would be melted for furtherrefining.

In all cases the pellets obtained are more or less spongy according tothe treatment given the pellets before reduction. Pellets which havebeen made with pure ferrie oxide land tlour binder and simply driedyield a very spongy product which disintegrates to any extremely tinepowder suitable for magnetic core production, while pellets which havebeen prepared with one half percent addition of alkaline or alkalineearth base and roasted at over 2000 F. yield on reduction a less spongypellet which disintegrates to a relatively coarse powder more suitablefor the fabrication of mechanical parts. All

afzeggen `,types-of lthe-resulting peliets however may bel simply meltedor pressed into cakes and then.v melted if solid metal is f required.

It-willbe understood that `various Yalternatives .and

1 equivalents may be used'for the ingredients of the charge.-

mixed with the-oxidized pellets .in the furnace. For example, in somecases instead of anthracite coal fines one may use `finely dividedbituminous coke or petroleum coke, whichfhas an ash with a high meltingpoint. In

vlieu of the sodium carbonate, one may use not only sov dium aluminatebut possibly other alkali metal or alkali earth metal carbonates orother catalysts which are known to have-the, property of intensifyingthe Vreaction of car-bon with oxygen. Also in lieu of the lime,limestone or dolomite,various other calcium compounds as well as othermaterials may bev used to prevent any sulphur present fromentering. thereduced iron.

Although preferred embodiments of the invention are herein disclosed forpurposes of explanation, various furl ther modifications thereof, afterstudy of the specification, will'be apparent to those skilled in the artto which the invention pertains.

Reference should accordingly be had to the appended claims indetermining the scope of 'the invention.

-What is claimed and desired to Ibe secured by Letters Patent is:

. l. Process-for reduction of iron oxide to form iron,

comprising first taking. finely divided iron oxide and forming same intohard porous pellets, mixing such pellets after-same have been formedwithfinely divided carbonaceousmaterial such that when burned will forman ash residue which is infusible at the reduction temperature of theprocess, the amount of such material being suiicientsubstantially.completely to reduce to ironthe iron about 2100? F. anduntil the iron oxide is reduced to iron, such temperature beingmaintained by the heat .evolved by the combustion, then conducting theresulting mixture includingthe reduced iron pellets and gaseous productsof reaction into a cooling zone, the atmosphere of which is maintainedwith an excess of carbon monoxide over dioxide whereby reoxidation ofthe pellets is avoided, and separating the reduced iron pellets from theremaining carbonaceous material and ash after discharge from saidcooling zone.

2. Process for reduction of iron oxide to form sponge iron, whichcomprises continuously introducing into a furnace the iron oxide inpelletilized form, and also fine- 1y divided carbonaceous fuel having alow hydrocarbon content and such that when burned will form a residuewhich is infnsible and does not sinter at the reduction temperature ofthe process, the amount of such fuel introduced being sufficientsubstantially completely to reduce t iron the iron oxide when reactedtherewith, and to provide an excess of carbon beyond that necessary forconverging carbon dioxide as evolved during the reaction largely tocarbon monoxide, such finely divided fuel and residue thereof providingan interfering phase between the pellets preventing them from stickingtogether during their reduction and permitting subsequent separationthereof from the fine material, introducing a supply of air limited tosubstantially the amount necessary to react with that amount of thecarbon present necessary to produce the heat required for reducing allof the oxide to iron, advancing the mixture including the air andgaseous products of combustion co-current through the furnace whileallowing the mixture to react at arternperature of from' about 1900:to.about 2100 F. and. until the iron oxide is reducedto iron,. andthencoolingithe resultingmixture including the reduced iron Vpellets in anon-oxidizing atmosphere.

3( Process in Vaccordance with the foregoing claim 2 and in which aquantity of a finely divided calcium compoundamounting to.20% or less byweight of thecarbon iofnthe fuel i's mixed withV thev furnace charge,for pre- Hventing any sulphur present lfrom entering the reduced iron.

4. Process in accordance with the 'foregoing claim 2 and in which asmall:quantity of finely Vdivided catalyst selected from: the rgroupcomprising sodium carbonate and sodium aluminate, amounting to about 1%or less by weight of the fuel," is mixed with the furnace charge wherebyhigher concentrations of carbon monoxide may be maintained at lowertemperatures in the furnace.

- 5. yProcessfor reduction of iron oxide to form sponge iron, whichcomprises continuously introducing the iron oxide in pelletilized forminto a furnace with finely divided carbonaceous fuel having a lowhydrocarbon content and such that when burned Will form a residue `whichis infusiblenand does not sinter atthe reduction temperature of` theprocess, the amount of such fuel introduced'being suicient substantiallycompletely to' reduce to iron the iron oxide when reacted therewith, andto providevan excessof carbon beyond the amount re- `quirediforconverting carbon dioxide as evolved during .f the reaction'largely tocarbon monoxide, introducing 2 with the mixture a supply of air limitedto substantially ythe amount necessary to generate about 1800 B. t; u.s

y per "pound of iron in the charge, by combustion of carbon therein tocarbon' monoxide, advancing the mixture including the air and'gaseousproducts of' combustion coeurrent through the Vfurnace while allowingthe' mixture to react at a temperature of from about 1900 to 'about2l`00 P anduntil the pelletilized oxide is reduced to iron pellets, andithen conductingthe resulting mixture including the reduced iron pellets,the excess fuel and residue into av cooling zone-and while the pelletsare being cooled therein, maintaining same in anatmosphere containingenough of thecarbon` monoxide 'evolved from Y the process topreventreoxidationiof the pellets.

6. Process for the reduction of ironoxide to iron,

-which comprises continuously introducing the viron oxide in apelletilizedrhard porous-formfinto` a rotary kiln iheated tonabout1900421005 F.,i together with finely divided anthracite coal, in theproportion of about pounds of the oxide to at least about 35 pounds ofthe coal, allowing the mixture to react to maintain such temperaturerange by introducing about 75 cubic feet of air for each pound of carbonin the coal and until the pelletilized oxide is reduced to iron pellets,and then cooling the resulting pellets while maintaining same in anon-oxidizing atmosphere.

7. Process for the reduction of iron oxide to iron, which comprisescontinuously introducing the iron oxide in a palletilized hard porousform into a furnace heated to about 1900-2100 F., together with finelydivided carbonaceous fuel having a low hydrocarbon content and such aswhen burned will form a residue which does not sinter in saidtemperature range, the oxide and carbon introduced being in theproportion of about 100 pounds of oxide to at least about 35 pounds ofcarbon, allowing the mixture to react by introducing only enough air tomaintain the temperature within about said range and until thepelletilized oxide is reduced to iron pellets, and then cooling theresulting pellets while maintaining same in an atmosphere which isnon-oxidizing in respect thereto.

8. Method for forming porous iron oxide pellets of a form adapted to bedirectly reduced to sponge iron on mixing and reacting with carbonaceousmaterial, which method comprises mixing with a mass of finely dividediron oxide which is incompletely oxidized, a small amount 1 1 of abinder material and a small amount of material selected from the groupcomprising soda ash, lime and magnesia, and also adding suiiicientmoisture to form a somewhat adherent mass, separating such mass intosmall lumps, forming such lumps into rounded pellets by advancing samethrough a rotating drum, gniting a mass of such pellets in a current ofair and allowing the re- Y sulting heat of oxidation to heat same to thepoint of incipient fusion and until same become hard and are largelyoxidized to ferric oxide.

9. Method for forming hard porous somewhat crystallized partiallyhollowed iron oxide pellets, which comprises mixing with finely dividedferrous oxide a small amount of a binder material and of a metallic basematerial together with suflicient moisture to form a somewhat adherentmass, separating said mass into small lumps, forming such lumps intorounded pellets by advancing same through a rotating drum, then ignitinga mass of the resulting pellets in a current of air and allowing theresulting heat of oxidation to bring same to substantially thetemperature of incipient fusion and until the same are oxidized toferrie oxide.

10. Method for forming hard porous iron oxide pellets of a form adaptedto be directly reduced to iron on mixing and reacting with carbonaceousmaterial, which method comprises mixing with a mass of finely dividedferric oxide a small quantity of powdered iron amounting to about 7% orless together with a small amount of binder material and sutiicientmoisture to form a somewhat adherent mass, separating such mass intosmall lumps, forming such lumps into rounded pellets by tumbling samc ina rotating drum, igniting a mass of such pellets in a current of air andallowing the resulting heat of oxidation of the powdered iron therein toheat same to the point of incipient fusion and until same become hard.

l1. Process for reduction of iron oxide to form iron,

, comprising first taking finely divided iron oxide material which isincompletely oxidized and mixing same with a small quantity of bindermaterial and sufficient moisture to form an adherent mass, separatingsuch mass into small lumps and tumbling such lumps to form roundedpellets, mixing such pellets with finely divided fuel and introducingthe mixture into a furnace heated to about 19002l00 F., the carbonaceousfuel selected being one having a low hydrocarbon content and such aswhen burned will form a residue which does not sinter in saidtemperature range, the oxide and carbon being introduced in the furnacein the proportion of about lbs. of oxide to at least about 35 lbs. ofcarbon, allowing the mixture to react by introducing only enough air tomaintain the temperature within about said range and until thepelletilized oxide is reduced to iron pellets, and then cooling theresulting pellets while maintaining same in an atmosphere non-oxidizingin respect thereto.

12. Process in accordance with claim 7 and in which the furnace chargeand gaseous products of combustion are advanced co-current through thefurnace, and the pellets are cooled in a cooling zone having anatmosphere containing suicient carbon monoxide evolved in the furnace tobe non-oxidizing with respect to the pellets.

13. Process for reduction of iron oxide to form iron by treating theoxide in a furnace with carbonaceous fuel, characterized by firstgrinding and forming the iron oxide into hardened porous pellets,introducing into the furnace such pelllets and also the fuel in a finelydivided form having a low hydrocarbon content and such that when burnedwill form a residue which is infusible and does not sinter at thereduction temperature of the process, the amount of such fuel introducedbeing in excess of that required substantially completely to reduce toiron the iron oxide when reacted therewith and to convert the carbondioxide as evolved during the reaction largely to carbon monoxide, thefinely divided fuel and residue thereof being of a character to providean interfering phase between the pellets preventing them from stickingtogether during the reaction and permitting subsequent separationthereof from the iinc material, also introducing a supply of air limitedsubstantially to the amount necessary to produce upon reacting with thecarbon the amount of heat required for reducing substantially all of theoxide to iron, advancing the pellets in adrnixture with the fuel andfuel residue in the furnace lfor a time and at a temperature sul'iicientto reduce the pellets to iron, and cooling the resulting mixture in anonoxidizing atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS1,777,993 Coley Oct. 7, 1930 1,937,822 Jones Dec. 5, 1933 2,026,683Johannsen Jan. 7, 1936 2,112,566 Hasselbach Mar. 29, 1938

1. PROCESS FOR REDUCTION OF IRON OXIDE TO FORM IRON, COMPRISING FIRSTTAKING FINELY DIVIDED IRON OXIDE AND FORMING SAME INTO HARD POROUSPELLETS, MIXING SUCH PELLETS AFTER SAME HAVE BEEN FORMED WITH FINELYDIVIDED CARBONACEOUS MATERIAL SUCH THAT WHEN BURNED WILL FORM AN ASHRESIDUE WHICH IS INFUSIBLE AT THE REDUCTION TEMPERATURE OF THE PROCESS,THE AMOUNT OF SUCH MATERIAL BEING SUFFICIENT SUBSTANTIALLY COMPLETELY TOREDUCE TO IRON THE IRON OXIDE WHEN REACTED THEREWITH AND TO LEAVE ENOUGHEXCESS OF CARBON FOR CONVERTING CARBON DIOXIDE EVELVED IN THE REACTION,TO CARBON MONOXIDE AND TO ACT AS AN INTERFERING PHASE BETWEEN THEPELLETS, CONTINUOUSLY CHARGING SUCH MIXTURE INTO A FURNACE, SUPPLYINGAIR INTO THE FURNACE LIMITED TO SUCH AMOUNT THAT THE ATMOSPHERE THEREINWILL CONTAIN AN AMOUNT OF MONOXIDE EQUAL AT LEAST TO ABOUT TWICE THECARBON DIOXIDE CONTENT, ALLOWING THE MIXTURE TO REACT AT A TEMPERATUREFROM ABOUT 1900 TO ABOUT 2100*F. AND UNTIL THE IRON OXIDE IS REDUCED TOIRON, SUCH TEMPERATURE BEING MAINTAINED BY THE HEAT EVOLVED BY THECOMBUSTION, THE CONDUCTING THE RESULTING MIXTURE INCLUDING THE REDUCEDIRON PELLETS AND GASEOUS PRODUCTS OF REACTION INTO A COOLING ZONE, THEATMOSPHERE OF WHICH IS MAINTAINED WITH AN EXCESS OF CARBON MONOXIDE OVERDIOXIDE WHEREBY REOXIDATION OF THE PELLETS IS AVOIDED, AND SEPARATINGTHE REDUCED IRON PELLETS FROM THE REMAINING CARBONACEOUS MATERIAL ANDASH AFTER DISCHARGE FROM SAID COOLING ZONE.